A power steering pump for an automotive vehicle comprises a pump for providing hydraulic fluid under pressure. U.S. Pat. No. 5,887,612, issued Bleitz et al. in 1999, shows a power steering pump of conventional design. The pump comprises a cam element sandwiched between upper and lower pressure plates that cooperate to form a cam chamber, and a rotor having retractable vanes located within the cam chamber. The arrangement of the cam element, upper and lower pressure plates and rotor is assembled within a housing that defines a suction passage for drawing fluid into the cam chamber through openings in the pressure plates and a discharge passage for receiving pumped fluid from the cam chamber through additional openings in the pressure plates. The housing includes an outlet communicating with the discharge passage for outputting pressurized fluid to the power steering system, and an inlet connected to a return line for cycling fluid back to the pump. A feature of the power steering pump described in Bleitz et al. is that the housing also defines a bypass that communicates with the suction passage, and a flow control mechanism. During operation, the rotor is driven by the engine through a belt and a pulley. At high engine speeds, the volume of pumped fluid is greater than the desired output for the system. Under these circumstances, the flow control mechanism diverts a portion of the pumped fluid from the output to the bypass passage which in turn leads to the suction passage. As much as 90% of the pumped fluid may be recycled internally within the pump through the bypass. The recycling of pumped fluid is critical to maintaining the pump output at the desired level for operation of the power steering system.
Conventional designs for power steering pumps thus require a large number of components that add significantly to the complexity and cost of the power steering pump. It is pointed out that the upper pressure plate includes openings for both the suction passage and the discharge passage, as also does the lower pressure plate. This arrangement for communicating with openings in both pressure plates further adds to the complexity of the design for the various passages within the housing.
Therefore, a need exists for a power steering pump that features a reduced number of components and a simpler design for the several passages for supplying, discharging and bypassing fluid.